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Can I install my battery

charger in the engine room

or compartment?

Mastervolt battery chargers can

easily be installed in the engine

room. Even at high temperatures,

Mastervolt battery chargers provide

the maximum charge current,

safely and quickly charging the

batteries. The output current will

be automatically reduced if the

ambient temperature becomes

very high.


Can I charge batteries


A number of models are fitted

with three outputs, allowing three

battery banks to be charged

independently of each other. Most

Mastervolt battery chargers have

an additional output for a starter

battery. This output supplies

for example the starter battery

with a maintenance charge. It is

also possible to charge multiple

battery sets via a battery isolator

(also known as a diode splitter).

The resulting voltage loss is

compensated by a setting in the

battery charger or by connecting

the battery sense cables.


Can the battery charger

be connected to the same

battery isolator as the


Although this is possible, it is better

and more convenient to fit two

separate battery isolators. If this

should be problematic, use the

battery isolator for both. In this

case, make sure that the battery

isolator or Battery Mate is powerful

enough to simultaneously handle

both the battery charger and

alternator current.


What should the cable diameter

be between the battery charger

and the battery?

When calculating the required diameter

of these cables follow this rule of thumb:

1 mm² of cable thickness for every 3

amps. A battery charger of 50 amps, for

instance, calls for a cable of 50:3 or 16.6

mm². The standard cable closest to this is

16 mm². This applies when the distance

is three metres at most. For longer

distances you will require a thicker cable.


What is the maximum distance

allowed between the battery

charger and the batteries?

In general, three metres is the maximum

length when you are using the calculation

method described earlier. A cable

length of 6 metres is also possible, but

thicker cables must then be used. The

previously provided example would

require 25 mm




Can I parallel connect a battery

charger to the alternator?

It is possible to parallel switch the battery

charger to an alternator of, for example,

the propulsion engine. This situation

occurs when the engine is running and a

230 V generator is started simultaneously.



Take an empty 200 Ah battery, a 50-

amp battery charger and a connected

load consuming 10 amps. Charging

time in this case would be around 200/

(50-10) = 5 h, or 9 h in total including

four hours of absorption time. If the

batteries are only half-discharged, the

recharge time would be 100/(50-10) =

2.5 + 4 h, 6.5 h in total. The absorption

time is shorter with Gel and AGM

batteries – around two to three hours.

These types of battery will therefore

recharge faster than conventional ones

(see also ‘Charging batteries’).


How long will it take before

my batteries are fully


The charging time of a battery is

directly related to the ratio of battery

to charger capacity. Other important

factors that decide how long it takes

for an empty battery to completely

recharge are the battery type and the

power consumption of the potential


As a rule of thumb for lead acid

batteries, divide the battery capacity

by the maximum charge capacity and

add four hours. The four hours are for

the absorption time, during which the

battery determines how much more

current is necessary and the battery

capacity increases from approx. 80 %

to 100 %.

Of course, this rule does not consider

the power consumption of other

connected equipment: If loads such as

a refrigerator or lights are connected,

their power consumption needs to be

subtracted from the available charge